Fuel injectors are well known for supplying a precisely metered amount of fuel to a fuel consuming device, for example, an internal combustion engine, where the fuel may be liquid or gaseous. The fuel injector generally includes a fuel inlet, a fuel outlet, and a valve member which is reciprocated to seat and unseat with a valve seat. Seating the valve member with the valve seat prevents fuel from flowing from the fuel inlet to the fuel outlet while unseating the valve member with the valve seat permits fuel to flow from the fuel inlet to the fuel outlet. A return spring is used to urge the valve member into contact with the valve seat while an actuator, commonly a solenoid, is used to apply a force to the valve member in order to unseat the valve member from the valve seat. In operation, when the actuator does not apply a force to the valve member, the return spring keeps the valve member seated with the valve seat, thereby preventing fuel from flowing from the fuel inlet to the fuel outlet. Conversely, when the actuator applies a force to the valve member, the valve member compresses the return spring and the valve member is unseated from the valve seat, thereby allowing fuel to flow from the fuel inlet to the fuel outlet. When the actuator ceases applying a force to the valve member, the return spring again urges the valve member to be seated with the valve seat.
The valve member is seated and unseated with the valve seat with high frequency, for example from four times per second to one hundred or even more times per second. Consequently, the time it takes the valve member to unseat (move the valve member from the seat to full open) and the time it takes the return spring to seat the valve member with the valve seat is important in determining the amount of fuel that is allowed to flow from the fuel inlet to the fuel outlet because if the valve member is unseated too quickly and seated too slowly due to low spring force, then too much fuel will be allowed to flow while if the valve member is unseated too slowly and seated too quickly due to high spring force, then not enough fuel will be allowed to flow. The force of the return spring determines the speed at which the valve member is opened and seated with the valve seat. Therefore, when the fuel injector is assembled, the force of the spring is deliberately set to achieve a desired dynamic flow through the fuel injector. As used herein, dynamic flow is the rate of flow of the fuel through the fuel injector over a period of time where the valve member is seated and unseated a plurality of times over the period of time. The spring force is set by adjusting the amount of compression that is applied to the return spring by a calibration tube. While the dynamic flow through the fuel injector is being monitored, the calibration tube is moved to change the amount of compression applied to the return spring until the desired dynamic flow rate is obtained.
It is known in the art of fuel injectors that the calibration tube mates with a fuel tube in a press fit relationship to fix the position of calibration tube in the fuel tube. It is also known in the art of fuel injectors that the fuel tube may include inwardly extending protrusions which mate with the calibration tube as will be described in greater detail below with reference to FIGS. 1 and 2. The protrusion create a spring fit between the calibration tube and the fuel tube, thereby However, as will also be described in greater detail below with reference to FIGS. 1 and 2, there may not be sufficient room on the fuel tube to provide inward protrusions of sufficient length to accommodate the range of axial positions of the calibration tube that may be needed to achieve the desired compression of the return spring.
What is needed is a fuel injector which minimizes or eliminates one or more of the shortcomings set forth above.